Cathodic pulses produce larger cochlear implant responses than anodic pulses across pulse shapes

Evidence

The morphology of the response was similar for acoustic and electric stimulation and consisted of a first positive peak (P1) followed by a negative peak (N1) and a second positive peak (P2). … It can be seen that at all current levels, the response was larger for the cathodic (RPS-IPG-C) than for the anodic (RPS-IPG-A) pulse. … A very large majority of the data points lie above the diagonal. This illustrates that so-called cathodic pulses usually produced a larger response than anodic pulses for all pulse shapes. — Dijk, Pim van, Physiology, Psychoacoustics and…, 2296

An alternative explanation for the higher anodic sensitivity at high current levels comes from a model of the implanted guinea-pig cochlea (Frijns et al. 1996 ). This model predicts that cathodic stimulation should elicit action potentials at the periphery of the neurons but that above a certain current level, the propagation of these action potentials may be blocked by the hyperpolarization produced more centrally on the fibers. This blocking was not observed in computer simulations using anodic stimuli because action potentials were in this case elicited at a more central locus on the fibers. A third aim of the present study was to investigate if this behavior could be observed at the level of the inferior colliculus of the guinea pigs. If, at some level in the dynamic range, action potentials are being blocked for cathodic stimulation, this should be reflected by a slower rate of increase of the neural response for cathodic than for anodic stimulation and/or potentially by a non-monotonic growth of response amplitude as a function of current level. — Dijk, Pim van, Physiology, Psychoacoustics and…, 2277

Categorization

• XREF: Connects to the reader’s interest in pulse-shape polarity effects in cochlear implant stimulation; also relevant to neural response polarity sensitivity literature in auditory physiology.
• SEED: The cathodic blocking hypothesis — where stimulation of the same polarity that excites the periphery also hyperpolarizes central fibers into conduction block — could ground an article on why cochlear implant polarity choice matters clinically.
• corroborated: 2 independent passages support this claim — Dijk, Pim van, Physiology, Psychoacoustics and…, 2296; Dijk, Pim van, Physiology, Psychoacoustics and…, 2277